Various conditions are addressed by fitting an eye with an intraocular lens to replace a natural crystalline lens of the eye. As well, contact lenses can be employed in correcting vision.
The human eye is known to naturally evolve in time. This evolution may change the geometry of the eye optics, the dynamics of its operation, its transmittance and accommodative capacity. Age related eye changes are described for example in “Age-Related Changes of the Human Eye” by Carlo A. P. Cavallotti, Luciano Cerulli, 2008, Springer. Changes in the geometry of the eye optics may be also be provoked by various interventions, such as eye surgery or a LASIK (Laser-Assisted in situ Keratomileusis) operation.
For example, development of a cataract (the decrease of eye's light transmission) is a common condition experienced with age. To improve light transmission, the eye is typically fitted with a plastic IntraOcular Lens (IOL) during cataract surgery, a well know medical procedure. Such an IOL may also be designed to adjust the total optical power of the eye. A goal of cataract surgery has long been to provide, postoperatively, unaided (without wearing glasses, including progressive ones) clear and high-quality distance, intermediate and near vision. However, such results are hard to attain. The current solutions do not enable dynamic distance accommodation capacity (controlled focus range); in fact cataract surgery may even degrade distance accommodation capacity:
Basic attempts to restore vision have included surgically empting a capsular bag, in which the natural crystalline lens of the eye resides, and refilling it with an accommodating polymer intended to match the behavior of a juvenile lens. While such attempts have received considerable attention, an effective actualization remains elusive today in part because properties of homogeneous polymers are insufficient to mimic properties of an inhomogeneous natural crystalline lens. In an article entitled “Accommodating IOLs: Emerging Concepts and Designs” published July 2004 in Cataract & Refractive Surgery Today, Samuel Masket MD describes difficulties in characterizing a crystalline lens in situ, which is subject to forces exerted by adjoining tissues, attesting to an inability to create an implant having desired properties under forces exerted by adjoining tissues postoperatively. Postoperative changes in adjoining tissues vary with the nature of the implant material and its contact with an anterior capsule of the eye. As well, any crystalline lens characterization is necessarily performed on an imperfect lens slated for invasive medical removal with the desire of providing a perfect intraocular prosthesis aided vision postoperatively. Even if a characterization of the crystalline lens from an earlier age would have been available, the surrounding tissues heal unevenly and also change with age rendering such characterization insufficient overall.
Implanting a fixed focus (monofocal) lens has been attempted in the prior art with a limited degree of success. Postoperatively, the combination of the remaining adjoining tissues and fixed focus lens provide only a limited degree of accommodation, compared to the juvenile natural lens, between 0.5 to 1.5 diopter pseudoaccommodation. In comparison, research by Mitchell Scheiman and Bruce Wick in “Clinical Management of Binocular Vision”, Lippincott, New York, 1994 suggests that on average a juvenile lens provides 18 diopters variability in average amplitude of accommodation. Generally, the average amplitude of accommodation at a given age may be estimated by Hofstetter's formula: 18.5 minus one third of the patient's age in years. Therefore, while a monofocal intraocular implant may provide clearer vision post operatively, the limited degree of post operative accommodation requires additional visual aids such as glasses or contact lenses. Dual optic prostheses have been implanted however suffer from low optical power variability in the range of 2.5 diopters.
Another example of a medical condition experienced by the majority of people with age is presbyopia (the loss of distance accommodation capacity). With age sufferers develop a flat eye lens, which is well adapted for distant vision, but not for mid or near distance vision.
Various flexible plastic monofocal lens systems were proposed, which rely on the mechanical deformation or a shift (such as Crystalens by Bausch & Lomb) induced by the muscular (such as ciliary) activity to provide variable optical power for dynamic distance accommodation. However, the ciliary muscle is a very complex organ (Johannes W. Rohen, “Scanning Electron Microscopic Studies of the Zonular Apparatus in Human and Monkey Eyes”, 1979 Assoc. for Res. In Vis. And Ophthal., inc., pp. 133-143), which constantly evolves with age and which is regarded too unreliable to propose solutions depending on it.
A further proposal includes multifocal IOLs, which have a diffractive structure and able to focus simultaneously far, mid and near distance objects on the retina. This however requires the brain to learn to select the appropriate zones. Multifocal IOLs may also produce visual side effects for distance vision and night vision; problems including glare, halos and the like.
Alternatively, electrically driven liquid lenses (U.S. Pat. No. 4,816,031; US 2007/0100443 A1) and liquid-crystal lenses (Elenza, U.S. Pat. No. 7,926,940; U.S. 61/441,863; “On the Possibility of Intraocular Adaptive Optics”, G. Vdovin et al., 7 Apr. 2003/Vol. 11, No. 7/OPTICS EXPRESS 810; “Liquid-Crystal Intraocular Adaptive Lens with Wireless Control”, A. N. Simonov et al., 11 Jun. 2007/Vol. 15, No. 12/OPTICS EXPRESS 7468) have been proposed as accommodative or Electrical IOLs (EIOLs). The optical power of such lenses may be changed gradually (by means of a tunable refractive lens) or in a discrete manner (by means of a tunable diffractive lens), see for example 14.5 L: Late-News Paper: “Comparisons Between a Liquid Crystal Refractive Lens and a Diffractive Lens for 3D Displays”, L. Lu et al., ISSN 0097-966X/11/4201-0171-$1.00 © 2011 SID, with the help of an electrical signal controlled by an Application Specific Integrated Circuit (ASIC) driver powered by a miniature remote chargeable battery.
Namely, tunable liquid crystal lenses have been proposed for use in active accommodation for example:
Tunable Liquid Crystal (TLC) optical devices are described, for example in International Patent Application publications WO/2007/098602 and WO/2009/153764. TLC optical devices are flat multi-layered structures having a Liquid Crystal (LC) layer. Good optical lens power can be achieved within a relatively small thickness. The liquid crystal layer has a (non-uniform) spatially modulated refractive index which changes in response to a spatially modulated electric field applied thereto. Moreover, liquid crystal refractive index variability is responsive to a time variable electric field. The principle of operation of the TLC optical device is the attenuation of the electrical potential, and the corresponding drop in electric field strength across an optical aperture between the periphery and the center of the TLC optical device. With an appropriate geometry, a variety of optical components employing TLC optical devices can be built, for example: a tunable lens, a corrective optical element, iris, etc. Tunable Liquid Crystal Lenses (TLCLs) provide significant advantages being thin and compact. The performance of TLCLs may be measured by a multitude of parameters, including: a tunable focus range, optical power (diopter) range, power consumption, transmittance, etc.